Disparity in the characteristic of thunderstorms and associated lightning activities over dissimilar terrains
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- Chaudhuri, S. & Middey, A. Meteorol Atmos Phys (2013) 119: 151. doi:10.1007/s00703-012-0226-4
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Thunderstorms and associated lightning flash activities are studied over two different locations in India with different terrain features. Lightning imaging sensor (LIS) data from 1998 to 2008 are analyzed during the pre-monsoon months (March, April and May). The eastern sector is designated as Sector A that represents a 2° × 2° square area enclosing Kolkata (22.65°N, 88.45°E) at the centre and covering Gangetic West Bengal, parts of Bihar and Orissa whereas the north-eastern sector designated as Sector B that also represents a 2° × 2° square area encircling Guwahati (26.10°N, 91.58°E) at the centre and covering Assam and foot hills of Himalaya of India. The stations Kolkata and Guwahati are selected for the present study from Sector A and Sector B, respectively, as these are the only stations over the selected areas having Radiosonde observatory. The result of the present study reveals that the characteristics of thunderstorms over the two locations are remarkably different. Lightning frequency is observed to be higher in Sector B than Sector A. The result further reveals that though the lightning frequency is less in Sector A, but the associated radiance is higher in Sector A than Sector B. It is also observed that the radiance increases linearly with convective available potential energy (CAPE) and their high correlation reveals that the lightning intensity can be estimated through the CAPE values. The sensitivity of lightning activity to CAPE is higher at the elevated station Guwahati (elevation 54 m) than Kolkata (elevation 6 m). Moderate resolution imaging spectrometer (MODIS) data products are used to obtain aerosol optical depth and cloud top temperature and employed to find their responses on lightning radiance.
Aerosol optical depth
Convective available potential energy
Cloud top temperature
Flash per minute
Lightning imaging sensor
Moderate resolution imaging spectrometer
Tropical rainfall measuring mission
The concern about natural disasters and severe weather like thunderstorm activities and lightning flashes necessitates the extensive research in this field. Over the Indian sub-continent, eastern and north-eastern parts are more prone to thunderstorms than the other parts of the country (IMD 1941; Guha and De 2009). Though thunderstorms may occur throughout the year (Manohar et al. 1999; Tyagi 2007), the thunderstorms of pre-monsoon period are most severe among all (Chaudhuri and Aich Bhowmick 2006). Every year immense damages on human lives, property, aviation and agriculture are observed due to high wind speed, lightning flashes, occasional hail and tornadoes and pulse rain associated with thunderstorms which cause enormous socio-economic impacts over the region. Initially, Koteswaram and Srinivasan (1958) pioneered the thunderstorm research over Gangetic West Bengal and concluded that concurrent existence of low level convergence and upper level divergence is the key factor for thunderstorm genesis. Mukherjee et al. (1964) studied extensively the thunderstorms over Guwahati and adjoining parts of north-eastern India and observed maximum frequency of thunderstorms during pre-monsoon months (March–May) particularly at night times. Kumar and Mohapatra (2006) observed that average of 5.4 squalls prevails during the pre-monsoon season over the region. Majority of thunderstorms was observed to occur during midnight to early morning over Guwahati and during afternoon to early night over Kolkata. The significance of storm updraft and strength can be well indicated by lightning flash rate (Baker et al. 1995). Reeve and Toumi (1999) observed that a change in the average land wet-bulb temperature of just 1 K over the globe would result in a change in lightning activity of about 40 %. There are number of climate studies using lightning and global electric circuit as global change indicator (Williams 1992; Price 1993; Gatlin and Goodman 2010). Williams (1985) did a pioneering work and established the dependence of lightning activity on the vertical development of convection. Gatlin and Goodman (2010) suggested lightning jump algorithm as a useful operational diagnostic tool for severe thunderstorm potential. The severe and most intense thunderstorm cells among the interacting storm cells within a mesoscale convective system (MCS) can be well diagnosed with lightning activity (Steiger et al. 2007). The microstructure of the cloud affects the lightning activity and the structure of the convective system (Timothy and Rutledge 2002; Khain et al. 2008). Various studies in this field have been done till date (Jacobson et al. 2007; Pessi et al. 2009; McCaul Jr. et al. 2009; Chaudhuri 2008a, b, 2010a, b, 2011a, b; Chaudhuri and Middey 2009, 2011a, b). Positive correlation between convective rainfall and lightning activity over central India has been identified during pre-monsoon months (Lal and Pawar 2009). The variations of lightning activity during tropical monsoon over three islands were studied by Ramesh Kumar and Kamra (2010) and concluded that the strengthening of updraft causes the increase in flash rate in a storm. Significant link between sea surface temperature in the bordering seas (Arabian sea and Bay of Bengal) and lightning activity over peninsular India has been established (Tinmaker et al. 2010) and on a seasonal time scale, two maxima of lightning activity one in May and another in September are found.
In the present study, an attempt is made to identify the disparity in the characteristics of thunderstorms and the associated lightning activities during the pre-monsoon season over the two different locations in India with different terrain features. Lightning imaging sensor (LIS) database from 1998 to 2008 is analyzed for the purpose. The eastern sector, Sector A (21.41°–24.55° latitude, 85.94°–89.3° longitude) covers the Gangetic West Bengal, adjoining part of Bihar and Orissa and the north-eastern sector, while Sector B (24.41°–26.6° latitude, 90.08°–94.04° longitude) covers Assam, foot hills of Himalaya. The aerosol optical depth (AOD) at 550 nm and cloud top temperature (CTT) are taken from moderate resolution imaging spectro-radiometer (MODIS) terra satellite to explore the microphysical effects on lightning activity and convective systems (Blyth et al. 2001). The present study can be used to categorize thunderclouds on the basis of microphysical characteristics, because it is evident that with lower AOD in thunderclouds of Kolkata the radiance of the lightning increases while the reverse situation prevails over Guwahati. The dissimilar microphysical characteristics during thunderstorm activity associated with lightning over Kolkata and Guwahati are the salient observations of the present study.
2 Materials and methods
The lightning data have been collected from the lightning imaging sensor (LIS) database during the period from 1998 to 2008 for the pre-monsoon months (March, April and May). The LIS is a TRMM satellite-based instrument and detects cloud-to-ground (CG) and intra cloud lightning activities within the troposphere. The TRMM satellite has circled the earth at an altitude of 350 km above the ground with an inclination of 35° since 1998. The TRMM satellite was boosted from an altitude of 350–402 km in August 2001 to extend its mission life. The primary component of LIS is a 128 × 128 charged coupled device (CCD) matrix, which has a sampling rate slightly greater than 500 frames per second. This lightning sensor locates and detects lightning flashes with storm-scale resolution (4–7 km) over a large region (600 km × 600 km) of the earth’s surface. The LIS sensor requires approximately 49 days to return to its original position relative to the Sun and the Earth, though the manual recommends using a 100-day window (Boccippio et al. 1998). LIS has a much smaller field of view, but has higher detection efficiency. A real time event processor (RTEP) removes the background signal and determines the time of occurrence, even in the presence of bright sunlit clouds, thus enabling the system to detect weak lightning and achieve 90 % detection efficiency (Koshak et al. 2000). The flash optical radiance observed by LIS is a measure of lightning discharge energy or the discharge current. In the present study, the data from the moderate resolution imaging spectro-radiometer (MODIS; King et al. 1992) are used to study the cloud top temperature (CTT) and aerosol optical depth (AOD) at 550 nm channel. The data set for March, April and May from 1998 to 2008 is collected from version 5 of MODIS terra satellite over Sector A and Sector B. The pre-monsoon thunderstorm records are collected from India Meteorological Department (IMD).
3 Results and discussions
The lightning activity (using LIS database) during the pre-monsoon months over two geographically different locations in India is studied with different thermodynamic and microphysical parameters; CAPE, cloud top temperature and aerosol optical depth collected from MODIS terra products. The genesis condition and dynamics for the development of thunderstorms over the two locations are observed to be completely different. Lightning activity is higher in Sector B than Sector A. Though the lightning frequency is comparatively less but the associated radiance is higher in Sector A than Sector B. Lightning radiances are representative of charge destroyed per lightning flash, and over Sector A these charge destruction processes are higher than that in Sector B. This may be due to the excess particulate matter present in the atmosphere over Sector A and during entrainment process the particulate matters get injected inside the clouds and because of radiative cooling the charge destruction processes facilitates (Kar et al. 2009). This is also evident from Figs. 15 and 16 that only at higher values of AOD the lightning radiances are higher over Sector B, but high lightning radiances are observed over Sector A even at low AOD. Special reference to the stations Kolkata (22.65°N, 88.45°E) and Guwahati (26.10°N, 91.58°E) belong to Sectors A and B, respectively, is made for thunderstorm and lightning activities. It is, thus, suggested that to forecast the lightning intensity over Sectors A and B, different schemes should be adopted for two zones as it is evident from the present study that lightning intensity and lightning radiance respond to the thermodynamic and dynamic parameters differently within Sectors A and B.
The first author acknowledges the India Meteorological Department (IMD), Govt. of India for providing the thunderstorm records and the respective websites for making the meteorological and satellite data available for scientific endeavour. The authors thank the anonymous reviewers for favourable comments and constructive suggestions which helped to improve the clarity of the paper.